Tauroursodeoxycholate (TUDCA), chemical chaperone, enhances function of islets by reducing ER stress

Nrf2 Signaling Pathway as a Key to Treatment for Diabetic Dyslipidemia and Atherosclerosis

Diabetes mellitus (DM) is a chronic endocrine disorder that affects more than 20 million people in the United States. DM-related complications affect multiple organ systems and are a significant cause of morbidity and mortality among people with DM. Of the numerous acute and chronic complications, atherosclerosis due to diabetic dyslipidemia is a condition that can lead to many life-threatening diseases, such as stroke, coronary artery disease, and myocardial infarction. The nuclear erythroid 2-related factor 2 (Nrf2) signaling pathway is an emerging antioxidative pathway and a promising target for the treatment of DM and its complications. This review aims to explore the Nrf2 pathway's role in combating diabetic dyslipidemia. We will explore risk factors for diabetic dyslipidemia at a cellular level and aim to elucidate how the Nrf2 pathway becomes a potential therapeutic target for DM-related atherosclerosis.

Collaborative Metabolism: Gut Microbes Play a Key Role in Canine and Feline Bile Acid Metabolism

Bile acids, produced by the liver and secreted into the gastrointestinal tract, are dynamic molecules capable of impacting the overall health of dogs and cats in many contexts. Importantly, the gut microbiota metabolizes host primary bile acids into chemically distinct secondary bile acids. This review explores the emergence of new literature connecting microbial-derived bile acid metabolism to canine and feline health and disease. Moreover, this review highlights multi-omic methodologies for translational research as an area for continued growth in veterinary medicine aimed at accelerating microbiome science and medicine as it pertains to bile acid metabolism in dogs and cats.

Tauroursodeoxycholic Acid Supplementation in In Vitro Culture of Indicine Bovine Embryos: Molecular and Cellular Effects on the In Vitro Cryotolerance

During embryo development, the endoplasmic reticulum (ER) acts as an important site for protein biosynthesis; however, in vitro culture (IVC) can negatively affect ER homeostasis. Therefore, the aim of our study was to evaluate the effects of the supplementation of tauroursodeoxycholic acid (TUDCA), an ER stress inhibitor, in the IVC of bovine embryos. Two experiments were carried out: Exp. 1: an evaluation of blastocyst rate, hatching kinetics, and gene expression of hatched embryos after being treated with different concentrations of TUDCA (50, 200, or 1000 μM) in the IVC; Exp. 2: an evaluation of the re-expansion, hatching, and gene expression of hatched embryos previously treated with 200 µM of TUDCA at IVC and submitted to vitrification. There was no increase in the blastocyst and hatched blastocyst rates treated with TUDCA in the IVC. However, embryos submitted to vitrification after treatment with 200 µM of TUDCA underwent an increased hatching rate post-warming together with a down-regulation in the expression of ER stress-related genes and the accumulation of lipids. In conclusion, this work showed that the addition of TUDCA during in vitro culture can improve the cryotolerance of the bovine blastocyst through the putative modulation of ER and oxidative stress.

Rapid Quantification of First and Second Phase Insulin Secretion Dynamics using an In vitro Platform for Improving Insulin Therapy

High-throughput quantification of the first- and second-phase insulin secretion dynamics is intractable with current methods. The fact that independent secretion phases play distinct roles in metabolism necessitates partitioning them separately and performing high-throughput compound screening to target them individually. We developed an insulin-nanoluc luciferase reporter system to dissect the molecular and cellular pathways involved in the separate phases of insulin secretion. We validated this method through genetic studies, including knockdown and overexpression, as well as small-molecule screening and their effects on insulin secretion. Furthermore, we demonstrated that the results of this method are well correlated with those of single-vesicle exocytosis experiments conducted on live cells, providing a quantitative reference for the approach. Thus, we have developed a robust methodology for screening small molecules and cellular pathways that target specific phases of insulin secretion, resulting in a better understanding of insulin secretion, which in turn will result in a more effective insulin therapy through the stimulation of endogenous glucose-stimulated insulin secretion.

Emerging Anti-Diabetic Drugs for Beta-Cell Protection in Type 1 Diabetes

Type 1 diabetes (T1D) is a chronic autoimmune disorder that damages beta cells in the pancreatic islets of Langerhans and results in hyperglycemia due to the loss of insulin. Exogenous insulin therapy can save lives but does not halt disease progression. Thus, an effective therapy may require beta-cell restoration and suppression of the autoimmune response. However, currently, there are no treatment options available that can halt T1D. Within the National Clinical Trial (NCT) database, a vast majority of over 3000 trials to treat T1D are devoted to insulin therapy. This review focuses on non-insulin pharmacological therapies. Many investigational new drugs fall under the category of immunomodulators, such as the recently FDA-approved CD-3 monoclonal antibody teplizumab. Four intriguing candidate drugs fall outside the category of immunomodulators, which are the focus of this review. Specifically, we discuss several non-immunomodulators that may have more direct action on beta cells, such as verapamil (a voltage-dependent calcium channel blocker), gamma aminobutyric acid (GABA, a major neurotransmitter with effects on beta cells), tauroursodeoxycholic acid (TUDCA, an endoplasmic reticulum chaperone), and volagidemab (a glucagon receptor antagonist). These emerging anti-diabetic drugs are expected to provide promising results in both beta-cell restoration and in suppressing cytokine-derived inflammation.

Endoplasmic Reticulum Stress: A Key Regulator of Cardiovascular Disease

The problems associated with economic development and social progress have led to an increase in the occurrence of cardiovascular diseases (CVDs), which affect the health of an increasing number of people and are a leading cause of disease and population mortality worldwide. Endoplasmic reticulum stress (ERS), a hot topic of interest for scholars in recent years, has been confirmed in numerous studies to be an important pathogenetic basis for many metabolic diseases and play an important role in maintaining physiological processes. The endoplasmic reticulum (ER) is a major organelle that is involved in protein folding and modification synthesis, and ERS occurs when several physiological and pathological factors allow excessive amounts of unfolded/misfolded proteins to accumulate. ERS often leads to initiation of the unfolded protein response (UPR) in a bid to re-establish tissue homeostasis; however, UPR has been documented to induce vascular remodeling and cardiomyocyte damage under various pathological conditions, leading to or accelerating the development of CVDs such as hypertension, atherosclerosis, and heart failure. In this review, we summarize the latest knowledge gained concerning ERS in terms of cardiovascular system pathophysiology, and discuss the feasibility of targeting ERS as a novel therapeutic target for the treatment of CVDs. Investigation of ERS has immense potential as a new direction for future research involving lifestyle intervention, the use of existing drugs, and the development of novel drugs that target and inhibit ERS.

Insights by which TUDCA is a potential therapy against adiposity

Adipose tissue is an organ with metabolic and endocrine activity. White, brown and ectopic adipose tissues have different structure, location, and function. Adipose tissue regulates energy homeostasis, providing energy in nutrient-deficient conditions and storing it in high-supply conditions. To attend to the high demand for energy storage during obesity, the adipose tissue undergoes morphological, functional and molecular changes. Endoplasmic reticulum (ER) stress has been evidenced as a molecular hallmark of metabolic disorders. In this sense, the ER stress inhibitor tauroursodeoxycholic acid (TUDCA), a bile acid conjugated to taurine with chemical chaperone activity, has emerged as a therapeutic strategy to minimize adipose tissue dysfunction and metabolic alterations associated with obesity. In this review, we highlight the effects of TUDCA and receptors TGR5 and FXR on adipose tissue in the setting of obesity. TUDCA has been demonstrated to limit metabolic disturbs associated to obesity by inhibiting ER stress, inflammation, and apoptosis in adipocytes. The beneficial effect of TUDCA on perivascular adipose tissue (PVAT) function and adiponectin release may be related to cardiovascular protection in obesity, although more studies are needed to clarify the mechanisms. Therefore, TUDCA has emerged as a potential therapeutic strategy for obesity and comorbidities.

Tauroursodeoxycholic Acid Inhibits Clostridioides difficile Toxin-Induced Apoptosis

C. difficile infection (CDI) is a highly inflammatory disease mediated by the production of two large toxins that weaken the intestinal epithelium and cause extensive colonic tissue damage. Antibiotic alternative therapies for CDI are urgently needed as current antibiotic regimens prolong the perturbation of the microbiota and lead to high disease recurrence rates. Inflammation is more closely correlated with CDI severity than bacterial burden, thus therapies that target the host response represent a promising yet unexplored strategy for treating CDI. Intestinal bile acids are key regulators of gut physiology that exert cytoprotective roles in cellular stress, inflammation, and barrier integrity, yet the dynamics between bile acids and host cellular processes during CDI have not been investigated. Here we show that several bile acids are protective against apoptosis caused by C. difficile toxins in Caco-2 cells and that protection is dependent on conjugation of bile acids. Out of 20 tested bile acids, taurine conjugated ursodeoxycholic acid (TUDCA) was the most potent inhibitor, yet unconjugated UDCA did not alter toxin-induced apoptosis. TUDCA treatment decreased expression of genes in lysosome associated and cytokine signaling pathways. TUDCA did not affect C. difficile growth or toxin activity in vitro whereas UDCA significantly reduced toxin activity in a Vero cell cytotoxicity assay and decreased tcdA gene expression. These results demonstrate that bile acid conjugation can have profound effects on C. difficile as well as the host and that conjugated and unconjugated bile acids may exert different therapeutic mechanisms against CDI.

ER stress and UPR in Alzheimer's disease: mechanisms, pathogenesis, treatments

Alzheimer's disease (AD) is a devastating neurodegenerative disorder characterized by gradual loss of memory and cognitive function, which constitutes a heavy burden on the healthcare system globally. Current therapeutics to interfere with the underlying disease process in AD is still under development. Although many efforts have centered on the toxic forms of Aβ to effectively tackle AD, considering the unsatisfactory results so far it is vital to examine other targets and therapeutic approaches as well. The endoplasmic reticulum (ER) stress refers to the build-up of unfolded or misfolded proteins within the ER, thus, perturbing the ER and cellular homeostasis. Emerging evidence indicates that ER stress contributes to the onset and development of AD. A thorough elucidation of ER stress machinery in AD pathology may help to open up new therapeutic avenues in the management of this devastating condition to relieve the cognitive dementia symptoms. Herein, we aim at deciphering the unique role of ER stress in AD pathogenesis, reviewing key findings, and existing controversy in an attempt to summarize plausible therapeutic interventions in the management of AD pathophysiology.

COVID-19 and Retinal Degenerative Diseases: Promising link “Kaempferol”

Coronavirus disease (COVID-19) outbreak has caused unprecedented global disruption since 2020. Approximately 238 million people are affected worldwide where the elderly succumb to mortality. Post-COVID syndrome and its side effects have popped up with several health hazards, such as macular degeneration and vision loss. It thus necessitates better medical care and management of our dietary practices. Natural flavonoids have been included in traditional medicine and have also been used safely against COVID-19 and several other diseases. Kaempferol is an essential flavonoid that has been demonstrated to influence several vital cellular signaling pathways involved in apoptosis, angiogenesis, inflammation, and autophagy. In this review, we emphasize the plausible regulatory effects of Kaempferol on hallmarks of COVID-19 and macular degeneration.

Characterization of amino acid substitutions and deletions in the kindlin-1 FERM domain: relevance for precision medicine

Kindler epidermolysis bullosa is a genodermatosis that manifests with cutaneous and mucosal fragility, and with photosensitivity. No cure is available to date. Kindlin-1, the deficient protein binds to β intergrin and is required for its activation. Using a previously established experimental workflow we addressed the consequences of three naturally occurring mutations leading either to single amino acid substitutions, p.Y293D and p.W559R, or to a single amino acid deletion p.I623del in kindlin-1. We show that p.Y293D disrupts kindlin-1 localization to focal adhesions and cell spreading. Although, treatment with a chemical chaperone increases the amount of mutant protein, spreading does not improve and cellular stress increases. In contrast, the mutations p.W559R and p.I623del do not interfere with kindlin-1 localization to focal adhesions and support cell adhesion and survival. These mutants are also responsive to the treatment with chemical chaperone, and the increased mutant proteins improve cell spreading. These findings suggest that low levels of mutant kindlins, p.W559R and p.I623del are able to rescue some important cellular functions. Patients carrying these mutations could benefit from treatment with promotors of proteostasis. Our results show that each mutation must be individually tested on genetic, molecular and cellular level to tailor personalized treatments for patients.

Pharmaceutical formulation and polymer chemistry for cell encapsulation applied to the creation of a lab-on-a-chip bio-microsystem

Microencapsulation of formulation designs further expands the field and offers the potential for use in developing bioartificial organs via cell encapsulation. Combining formulation design and encapsulation requires ideal excipients to be determined. In terms of cell encapsulation, an environment which allows growth and functionality is paramount to ensuring cell survival and incorporation into a bioartificial organ. Hence, excipients are examined for both individual properties and benefits, and compatibility with encapsulated active materials. Polymers are commonly used in microencapsulation, offering protection from the immune system. Bile acids are emerging as a tool to enhance delivery, both biologically and pharmaceutically. Therefore, this review will focus on bile acids and polymers in formulation design via microencapsulation, in the field of bioartificial organ development.

Oxidative Stress Leads to β-Cell Dysfunction Through Loss of β-Cell Identity

Pancreatic β-cell failure is a critical event in the onset of both main types of diabetes mellitus but underlying mechanisms are not fully understood. β-cells have low anti-oxidant capacity, making them more susceptible to oxidative stress. In type 1 diabetes (T1D), reactive oxygen species (ROS) are associated with pro-inflammatory conditions at the onset of the disease. Here, we investigated the effects of hydrogen peroxide-induced oxidative stress on human β-cells. We show that primary human β-cell function is decreased. This reduced function is associated with an ER stress response and the shuttling of FOXO1 to the nucleus. Furthermore, oxidative stress leads to loss of β-cell maturity genes MAFA and PDX1, and to a concomitant increase in progenitor marker expression of SOX9 and HES1. Overall, we propose that oxidative stress-induced β-cell failure may result from partial dedifferentiation. Targeting antioxidant mechanisms may preserve functional β-cell mass in early stages of development of T1D.

Endoplasmic reticulum stress response and bile acid signatures associate with multi-strain seroresponsiveness during elderly influenza vaccination

The elderly are an important target for influenza vaccination, and the determination of factors that underlie immune responsiveness is clinically valuable. We evaluated the immune and metabolic profiles of 205 elderly Singaporeans administered with Vaxigrip. Despite high seroprotection rates, we observed heterogeneity in the response. We stratified the cohort into complete (CR) or incomplete responders (IR), where IR exhibited signs of accelerated T cell aging. We found a higher upregulation of genes associated with the B-cell endoplasmic-reticulum stress response in CR, where XBP-1 acts as a key upstream regulator. B-cells from IR were incapable of matching the level of XBP-1 upregulation observed in CR after inducing ER stress with tunicamycin in vitro. Metabolic signatures also distinguished CR and IR - as CR presented with a greater diversity of bile acids. Our findings suggest that the ER-stress pathway activation could improve influenza vaccination in the elderly.

Chenodeoxycholic Acid Pharmacology in Biotechnology and Transplantable Pharmaceutical Applications for Tissue Delivery: An Acute Preclinical Study

INTRODUCTION

Primary bile acids (PBAs) are produced and released into human gut as a result of cholesterol catabolism in the liver. A predominant PBA is chenodeoxycholic acid (CDCA), which in a recent study in our laboratory, showed significant excipient-stabilizing effects on microcapsules carrying insulinoma β-cells, in vitro, resulting in improved cell functions and insulin release, in the hyperglycemic state. Hence, this study aimed to investigate the applications of CDCA in bio-encapsulation and transplantation of primary healthy viable islets, preclinically, in type 1 diabetes.

METHODS

Healthy islets were harvested from balb/c mice, encapsulated in CDCA microcapsules, and transplanted into the epididymal tissues of 6 syngeneic diabetic mice, post diabetes confirmation. Pre-transplantation, the microcapsules' morphology, size, CDCA-deep layer distribution, and physical features such as swelling ratio and mechanical strength were analyzed. Post-transplantation, animals' weight, bile acids', and proinflammatory biomarkers' concentrations were analyzed. The control group was diabetic mice that were transplanted encapsulated islets (without PBA).

RESULTS AND CONCLUSION

Islet encapsulation by PBA microcapsules did not compromise the microcapsules' morphology or features. Furthermore, the PBA-graft performed better in terms of glycemic control and resulted in modulation of the bile acid profile in the brain. This is suggestive that the improved glycemic control was mediated via brain-related effects. However, the improvement in graft insulin delivery and glycemic control was short-term.

Advancements in Assessments of Bio-Tissue Engineering and Viable Cell Delivery Matrices Using Bile Acid-Based Pharmacological Biotechnologies

The utilisation of bioartificial organs is of significant interest to many due to their versatility in treating a wide range of disorders. Microencapsulation has a potentially significant role in such organs. In order to utilise microcapsules, accurate characterisation and analysis is required to assess their properties and suitability. Bioartificial organs or transplantable microdevices must also account for immunogenic considerations, which will be discussed in detail. One of the most characterized cases is the investigation into a bioartificial pancreas, including using microencapsulation of islets or other cells, and will be the focus subject of this review. Overall, this review will discuss the traditional and modern technologies which are necessary for the characterisation of properties for transplantable microdevices or organs, summarizing analysis of the microcapsule itself, cells and finally a working organ. Furthermore, immunogenic considerations of such organs are another important aspect which is addressed within this review. The various techniques, methodologies, advantages, and disadvantages will all be discussed. Hence, the purpose of this review is providing an updated examination of all processes for the analysis of a working, biocompatible artificial organ.

Effects of Cell Proteostasis Network on the Survival of SARS-CoV-2

The proteostasis network includes all the factors that control the function of proteins in their native state and minimize their non-functional or harmful reactions. The molecular chaperones, the important mediator in the proteostasis network can be considered as any protein that contributes to proper folding and assembly of other macromolecules, through maturating of unfolded or partially folded macromolecules, refolding of stress-denatured proteins, and modifying oligomeric assembly, otherwise it leads to their proteolytic degradation. Viruses that use the hosts' gene expression tools and protein synthesis apparatus to survive and replicate, are obviously protected by such a host chaperone system. This means that many viruses use members of the hosts' chaperoning system to infect the target cells, replicate, and spread. During viral infection, increase in endoplasmic reticulum (ER) stress due to high expression of viral proteins enhances the level of heat shock proteins (HSPs) and induces cell apoptosis or necrosis. Indeed, evidence suggests that ER stress and the induction of unfolded protein response (UPR) may be a major aspect of the corona-host virus interaction. In addition, several clinical reports have confirmed the autoimmune phenomena in COVID-19-patients, and a strong association between this autoimmunity and severe SARS-CoV-2 infection. Part of such autoimmunity is due to shared epitopes among the virus and host. This article reviews the proteostasis network and its relationship to the immune system in SARS-CoV-2 infection.

Treatment of in vitro-Matured Bovine Oocytes With Tauroursodeoxycholic Acid Modulates the Oxidative Stress Signaling Pathway

In several species, oocyte and embryo competence are improved by the addition of endoplasmic reticulum (ER) stress inhibitors to in vitro maturation (IVM) medium and/or in vitro culture (IVC) medium. This study aimed to evaluate the effects of three concentrations of tauroursodeoxycholic acid (TUDCA; 50, 200, and 1,000 μM), a chemical chaperone for relieving ER stress, during IVM of bovine cumulus-oocyte complexes (COCs) for 24 h. Treated oocytes were analyzed for nuclear maturation, reactive oxygen species (ROS) production, mitochondrial activity, and abundance of target transcripts. In addition, the number of pronuclei in oocytes was evaluated after 18-20 h of insemination, and the rates of blastocyst and hatched blastocyst formation were evaluated after 7 and 8/9 days of culture, respectively. We further evaluated the transcript abundance of embryonic quality markers. Our findings showed that supplementation of IVM medium with 200 μM of TUDCA decreased ROS production and increased abundance of transcripts related to antioxidant activity in oocytes (CAT, GPX1, and HMOX1) and embryos (GPX1 and PRDX3). Interestingly, high concentration of TUDCA (1,000 μM) was toxic to oocytes, reducing the nuclear maturation rate, decreasing mitochondrial activity, and increasing the abundance of ER stress (HSPA5) and cellular apoptosis (CASP3 and CD40) related transcripts. The results of this study suggest that treatment with 200 μM of TUDCA is associated with a greater resistance to oxidative stress and indirectly with ER stress relief in bovine oocytes.

Secondary bile acid ursodeoxycholic acid alters weight, the gut microbiota, and the bile acid pool in conventional mice

Ursodeoxycholic acid (commercially available as ursodiol) is a naturally occurring bile acid that is used to treat a variety of hepatic and gastrointestinal diseases. Ursodiol can modulate bile acid pools, which have the potential to alter the gut microbiota community structure. In turn, the gut microbial community can modulate bile acid pools, thus highlighting the interconnectedness of the gut microbiota-bile acid-host axis. Despite these interactions, it remains unclear if and how exogenously administered ursodiol shapes the gut microbial community structure and bile acid pool in conventional mice. This study aims to characterize how ursodiol alters the gastrointestinal ecosystem in conventional mice. C57BL/6J wildtype mice were given one of three doses of ursodiol (50, 150, or 450 mg/kg/day) by oral gavage for 21 days. Alterations in the gut microbiota and bile acids were examined including stool, ileal, and cecal content. Bile acids were also measured in serum. Significant weight loss was seen in mice treated with the low and high dose of ursodiol. Alterations in the microbial community structure and bile acid pool were seen in ileal and cecal content compared to pretreatment, and longitudinally in feces following the 21-day ursodiol treatment. In both ileal and cecal content, members of the Lachnospiraceae Family significantly contributed to the changes observed. This study is the first to provide a comprehensive view of how exogenously administered ursodiol shapes the healthy gastrointestinal ecosystem in conventional mice. Further studies to investigate how these changes in turn modify the host physiologic response are important.

The bile acid TUDCA improves glucose metabolism in streptozotocin-induced Alzheimer's disease mice model

Alzheimer's disease (AD) is a neurodegenerative disorder and the major cause of dementia. According to predictions of the World Health Organization, more than 150 million people worldwide will suffer from dementia by 2050. An increasing number of studies have associated AD with type 2 diabetes mellitus (T2DM), since most of the features found in T2DM are also observed in AD, such as insulin resistance and glucose intolerance. In this sense, some bile acids have emerged as new therapeutic targets to treat AD and metabolic disorders. The taurine conjugated bile acid, tauroursodeoxycholic (TUDCA), reduces amyloid oligomer accumulation and improves cognition in APP/PS1 mice model of AD, and also improves glucose-insulin homeostasis in obese and type 2 diabetic mice. Herein, we investigated the effect of TUDCA upon glucose metabolism in streptozotocin-induced AD mice model (Stz). The Stz mice that received 300 mg/kg TUDCA during 10 days (Stz + TUDCA), showed improvement in glucose tolerance and insulin sensitivity, reduced fasted and fed glycemia, increased islet mass and β-cell area, as well as increased glucose-stimulated insulin secretion, compared with Stz mice that received only PBS. Stz + TUDCA mice also displayed lower neuroinflammation, reduced protein content of amyloid oligomer in the hippocampus, improved memory test and increased protein content of insulin receptor β-subunit in the hippocampus. In conclusion, TUDCA treatment enhanced glucose homeostasis in the streptozotocin-induced Alzheimer's disease mice model, pointing this bile acid as a good strategy to counteract glucose homeostasis disturbance in AD pathology.

TUDCA inhibits HSV-1 replication by the modulating unfolded protein response pathway

Tauroursodeoxycholic acid (TUDCA), an endogenous bile acid, was used to protect liver function through antiapoptosis or reducing endoplasmic reticulum stress (ER stress). Previous studies showed that ER stress was modulated by herpes simplex virus types 1 (HSV-1) infection to facilitate viral replication. Here, we investigated the effect of TUDCA on HSV-1 infection of HEC-1-A cells and showed that both replication and multiplication of the virus were inhibited by TUDCA in a dose dependent manner. Unfolded protein response was induced to deliver stress signals from ER to nucleus. We found that TUDCA alleviated activating transcription factor 6 branch inhibition, partially enhanced protein kinase RNA-like ER kinase pathway activation, and repressed inositol-requiring protein 1α arm activation significantly in infected cells. The findings of this study suggest that TUDCA inhibits HSV-1 replication through ER stress pathway, which may provide a potential therapeutic strategy for HSV-1 infection.

Endoplasmic reticulum stress-related neuroinflammation and neural stem cells decrease in mice exposure to paraquat

Paraquat (PQ), a widely used herbicide, could cause neurodegenerative diseases, yet the mechanism remains incompletely understood. This study aimed to investigate the direct effect of PQ on NSC in vivo and its possible mechanism. Adult C57BL/6 mice were subcutaneously injected with 2 mg/kg PQ, 20 mg/kg PQ or vehicle control once a week for 2 weeks, and sacrificed 1 week after the last PQ injection. Furthermore, extra experiments with Tauroursodeoxycholic Acid (TUDCA) intervention were performed to observe the relationship between ER stress, neuroinflammation and the neural stem cell (NSC) impairment. The results showed that 20 mg/kg PQ caused the NSC number decrease in both subgranular zones (SGZ) and subventricular zone (SVZ). Further analysis indicated that the 20 mg/kg PQ suppressed the proliferation of NSC, without affecting the apoptosis. Moreover, 20 mg/kg PQ also induced ER stress in microglia and caused neuroinflammation in SGZ and SVZ. Interestingly, the ER stress inhibitor could simultaneously ameliorate the neuroinflammation and NSC reduction. These data suggested that increased ER stress in microglia might be a possible pathway for PQ-induced neuroinflammation and NSC impairment. That is a previously unknown mechanism for PQ neurotoxicity.

Bax and Bak jointly control survival and dampen the early unfolded protein response in pancreatic β-cells under glucolipotoxic stress

ER stress and apoptosis contribute to the loss of pancreatic β-cells under pro-diabetic conditions of glucolipotoxicity. Although activation of canonical intrinsic apoptosis is known to require pro-apoptotic Bcl-2 family proteins Bax and Bak, their individual and combined involvement in glucolipotoxic β-cell death are not known. It has also remained an open question if Bax and Bak in β-cells have non-apoptotic roles in mitochondrial function and ER stress signaling, as suggested in other cell types. Using mice with individual or combined β-cell deletion of Bax and Bak, we demonstrated that glucolipotoxic β-cell death in vitro occurs by both non-apoptotic and apoptotic mechanisms, and the apoptosis could be triggered by either Bax or Bak alone. In contrast, they had non-redundant roles in mediating staurosporine-induced apoptosis. We further established that Bax and Bak do not affect normal glucose-stimulated β-cell Ca²⁺ responses, insulin secretion, or in vivo glucose tolerance. Finally, our experiments revealed that combined deletion of Bax and Bak amplified the unfolded protein response in islets during the early stages of chemical- or glucolipotoxicity-induced ER stress. These findings shed new light on roles of the core apoptosis machinery in β-cell survival and stress signals of importance for the pathobiology of diabetes.

Endoplasmic reticulum-mediated unfolded protein response is an integral part of singlet oxygen signalling in plants

Singlet oxygen (¹ O₂ ) is a by-product of photosynthesis that triggers a signalling pathway leading to stress acclimation or to cell death. By analyzing gene expressions in a ¹ O₂ -overproducing Arabidopsis mutant (ch1) under different light regimes, we show here that the ¹ O₂ signalling pathway involves the endoplasmic reticulum (ER)-mediated unfolded protein response (UPR). ch1 plants in low light exhibited a moderate activation of UPR genes, in particular bZIP60, and low concentrations of the UPR-inducer tunicamycin enhanced tolerance to photooxidative stress, together suggesting a role for UPR in plant acclimation to low ¹ O₂ levels. Exposure of ch1 to high light stress ultimately leading to cell death resulted in a marked upregulation of the two UPR branches (bZIP60/IRE1 and bZIP28/bZIP17). Accordingly, mutational suppression of bZIP60 and bZIP28 increased plant phototolerance, and a strong UPR activation by high tunicamycin concentrations promoted high light-induced cell death. Conversely, light acclimation of ch1 to ¹ O₂ stress put a limitation in the high light-induced expression of UPR genes, except for the gene encoding the BIP3 chaperone, which was selectively upregulated. BIP3 deletion enhanced Arabidopsis photosensitivity while plants treated with a chemical chaperone exhibited enhanced phototolerance. In conclusion, ¹ O₂ induces the ER-mediated UPR response that fulfils a dual role in high light stress: a moderate UPR, with selective induction of BIP3, is part of the acclimatory response to ¹ O₂ , and a strong activation of the whole UPR is associated with cell death.

Rescue of HSP70 in Spinal Neurons Alleviates Opioids-Induced Hyperalgesia via the Suppression of Endoplasmic Reticulum Stress in Rodents

A major unresolved issue in treating pain is the paradoxical hyperalgesia produced by the gold-standard analgesic morphine and other opioids. Endoplasmic reticulum (ER) stress has been shown to contribute to neuropathic or inflammatory pain, but its roles in opioids-induced hyperalgesia (OIH) are elusive. Here, we provide the first direct evidence that ER stress is a significant driver of OIH. GRP78, the ER stress marker, is markedly upregulated in neurons in the spinal cord after chronic morphine treatment. At the same time, morphine induces the activation of three arms of unfolded protein response (UPR): inositol-requiring enzyme 1α/X-box binding protein 1 (IRE1α/XBP1), protein kinase RNA-like ER kinase/eukaryotic initiation factor 2 subunit alpha (PERK/eIF2α), and activating transcription factor 6 (ATF6). Notably, we found that inhibition on either IRE1α/XBP1 or ATF6, but not on PERK/eIF2α could attenuate the development of OIH. Consequently, ER stress induced by morphine enhances PKA-mediated phosphorylation of NMDA receptor subunit 1(NR1) and leads to OIH. We further showed that heat shock protein 70 (HSP70), a molecular chaperone involved in protein folding in ER, is heavily released from spinal neurons after morphine treatment upon the control of K_ATP channel. Glibenclamide, a classic K_ATP channel blocker that inhibits the efflux of HSP70 from cytoplasm to extracellular environment, or HSP70 overexpression in neurons, could markedly suppress morphine-induced ER stress and hyperalgesia. Taken together, our findings uncover the induction process and the central role of ER stress in the development of OIH and support a novel strategy for anti-OIH treatment.

Endoplasmic Reticulum (ER) Stress Inhibitor or Antioxidant Treatments during Micromanipulation Can Inhibit Both ER and Oxidative Stresses in Porcine SCNT Embryos

We investigated the effects of endoplasmic reticulum (ER) stress inhibitor and antioxidant treatments during the micromanipulation of somatic cell nuclear transfer (SCNT) on in vitro development of SCNT embryos. Tauroursodeoxycholic acid (TUDCA), an ER stress inhibitor and vitamin C (Vit. C), an antioxidant, were treated by alone or in combination, then, the level of X-box binding protein 1 (Xbp1) splicing and the expressions of ER stress-associated genes, oxidative stress-related genes, and apoptotic genes were confirmed in the 1-cell and blastocyst stages. In the 1-cell stage, the levels of Xbp1 splicing were significantly decreased in TUDCA and Vit. C treatment groups compared to the control (p<0.05). In addition, the expression levels of most ER stress-associated genes and oxidative stress-related genes were significantly lower in all treatment groups than the control (p<0.05), and the transcript levels of apoptotic genes were also significantly lower in all treatment groups than the control (p<0.05). In the blastocyst stage, decreased expression of ER stress-, oxidative stress-, and apoptosis-related genes were observed only in some treatments. However, the blastocyst formation rates in TUDCA and Vit. C treatment groups (24.8% and 22.0%, respectively) and mean blastocyst cell number in all treatment groups (59.7±4.3 to 63.5±3.3) were significantly higher (p<0.05) than those of control. The results showed that the TUDCA or Vit. C treatment during micromanipulation inhibited both ER and oxidative stresses in the early stage of SCNT embryos, thereby reducing cell damage and promoting in vitro development.

Endoplasmic reticulum stress and pulmonary hypertension

Pulmonary hypertension is a fatal disease of which pulmonary vasculopathy is the main pathological feature resulting in the mean pulmonary arterial pressure higher than 25 mmHg. Moreover, pulmonary hypertension remains a tough problem with unclear molecular mechanisms. There have been dozens of studies about endoplasmic reticulum stress during the onset of pulmonary hypertension in patients, suggesting that endoplasmic reticulum stress may have a critical effect on the pathogenesis of pulmonary hypertension. The review aims to summarize the rationale to elucidate the role of endoplasmic reticulum stress in pulmonary hypertension. Started by reviewing the mechanisms responsible for the unfolded protein response following endoplasmic reticulum stress, the potential link between endoplasmic reticulum stress and pulmonary hypertension were introduced, and the contributions of endoplasmic reticulum stress to different vascular cells, mitochondria, and inflammation were described, and finally the potential therapies of attenuating endoplasmic reticulum stress for pulmonary hypertension were discussed.

Bile acids in glucose metabolism and insulin signalling - mechanisms and research needs

Of all the novel glucoregulatory molecules discovered in the past 20 years, bile acids (BAs) are notable for the fact that they were hiding in plain sight. BAs were well known for their requirement in dietary lipid absorption and biliary cholesterol secretion, due to their micelle-forming properties. However, it was not until 1999 that BAs were discovered to be endogenous ligands for the nuclear receptor FXR. Since that time, BAs have been shown to act through multiple receptors (PXR, VDR, TGR5 and S1PR2), as well as to have receptor-independent mechanisms (membrane dynamics, allosteric modulation of N-acyl phosphatidylethanolamine phospholipase D). We now also have an appreciation of the range of physiological, pathophysiological and therapeutic conditions in which endogenous BAs are altered, raising the possibility that BAs contribute to the effects of these conditions on glycaemia. In this Review, we highlight the mechanisms by which BAs regulate glucose homeostasis and the settings in which endogenous BAs are altered, and provide suggestions for future research.

Tauroursodeoxycholate-Bile Acid with Chaperoning Activity: Molecular and Cellular Effects and Therapeutic Perspectives

Tauroursodeoxycholic acid (TUDCA) is a naturally occurring hydrophilic bile acid that has been used for centuries in Chinese medicine. Chemically, TUDCA is a taurine conjugate of ursodeoxycholic acid (UDCA), which in contemporary pharmacology is approved by Food and Drug Administration (FDA) for treatment of primary biliary cholangitis. Interestingly, numerous recent studies demonstrate that mechanisms of TUDCA functioning extend beyond hepatobiliary disorders. Thus, TUDCA has been demonstrated to display potential therapeutic benefits in various models of many diseases such as diabetes, obesity, and neurodegenerative diseases, mostly due to its cytoprotective effect. The mechanisms underlying this cytoprotective activity have been mainly attributed to alleviation of endoplasmic reticulum (ER) stress and stabilization of the unfolded protein response (UPR), which contributed to naming TUDCA as a chemical chaperone. Apart from that, TUDCA has also been found to reduce oxidative stress, suppress apoptosis, and decrease inflammation in many in-vitro and in-vivo models of various diseases. The latest research suggests that TUDCA can also play a role as an epigenetic modulator and act as therapeutic agent in certain types of cancer. Nevertheless, despite the massive amount of evidence demonstrating positive effects of TUDCA in pre-clinical studies, there are certain limitations restraining its wide use in patients. Here, molecular and cellular modes of action of TUDCA are described and therapeutic opportunities and limitations of this bile acid are discussed.

Control of Protein Homeostasis in the Early Secretory Pathway: Current Status and Challenges

: Discrimination between properly folded proteins and those that do not reach this state is necessary for cells to achieve functionality. Eukaryotic cells have evolved several mechanisms to ensure secretory protein quality control, which allows efficiency and fidelity in protein production. Among the actors involved in such process, both endoplasmic reticulum (ER) and the Golgi complex play prominent roles in protein synthesis, biogenesis and secretion. ER and Golgi functions ensure that only properly folded proteins are allowed to flow through the secretory pathway while improperly folded proteins have to be eliminated to not impinge on cellular functions. Thus, complex quality control and degradation machineries are crucial to prevent the toxic accumulation of improperly folded proteins. However, in some instances, improperly folded proteins can escape the quality control systems thereby contributing to several human diseases. Herein, we summarize how the early secretory pathways copes with the accumulation of improperly folded proteins, and how insufficient handling can cause the development of several human diseases. Finally, we detail the genetic and pharmacologic approaches that could be used as potential therapeutic tools to treat these diseases.

Alteration in bile acids profile in Large White pigs during chronic heat exposure

Bile acids (BAs) are critical for cholesterol homeostasis and new roles in metabolism and endocrinology have been demonstrated recently. It remains unknown whether BA metabolism can be affected by heat stress (HS). The objective of this study was to describe the shifts in serum, hepatic and intestinal BA profiles induced by chronic HS. Twenty-seven Large White pigs weighing 40.8 ± 2.7 kg were assigned to one of the three treatments: a control group (CON, 23 °C), a HS group (33 °C), or a pair-fed group (PF, 23 °C and fed the same amount as HS group) for 21 d. The concentrations of taurine-conjugated BAs (TUDCA and THDCA in serum and TCDCA, TUDCA, THDCA and THCA in liver) were decreased in HS and PF pigs. However, in HS pigs, a reduction in taurine-conjugated BAs (TCBA) correlated with decreased liver genes expression of BA synthesis, conjugation and uptake transport. BA regulated-genes (FXR, TGR5 and FGFR4) in HS pigs and TGR5, FGFR4 and KLβ in PF pigs were down-regulated in liver. In ileum, total BAs and glycoursodeoxycholic acid concentrations were higher in HS pigs than other groups and PF group, respectively (P < 0.05). TCBA (P = 0.01) and tauroursodeoxycholic acid (P < 0.01) were decreased in PF group. BA transporters (OSTα and MRP3) were up-regulated in HS pigs compared with CON and PF pigs, respectively (P < 0.01). In cecum, ursodeoxycholic acid was higher in HS (P = 0.02) group than CON group. The expression of apical sodium-coupled bile acid transporter (P = 0.04) was lower in HS pigs than CON pigs, while OSTβ (P < 0.01) was greater in HS group than PF group. These results suggest that chronic HS suppressed liver activity of synthesis and uptake of TCBA, at least in part, which was independent of reduced feed intake.

GRP78 translocation to the cell surface and O-GlcNAcylation of VE-Cadherin contribute to ER stress-mediated endothelial permeability

Increased O-GlcNAcylation, a well-known post-translational modification of proteins causally linked to various detrimental cellular functions in pathological conditions including diabetic retinopathy (DR). Previously we have shown that endothelial activation induced by inflammation and hyperglycemia results in the endoplasmic reticulum (ER) stress-mediated intercellular junction alterations accompanied by visual deficits in a tie2-TNF-α transgenic mouse model. In this study, we tested the hypothesis that increased ER stress via O-GlcNAcylation of VE-Cadherin likely contribute to endothelial permeability. We show that ER stress leads to GRP78 translocation to the plasma membrane, increased O-GlcNAcylation of proteins, particularly VE-Cadherin resulting in a defective complex partnering leading to the loss of retinal endothelial barrier integrity and increased transendothelial migration of monocytes. We further show an association of GRP78 with the VE-Cadherin under these conditions. Interestingly, cells exposed to ER stress inhibitor, tauroursodeoxycholic acid partially mitigated all these effects. Our findings suggest an essential role for ER stress and O-GlcNAcylation in altering the endothelial barrier function and reveal a potential therapeutic target in the treatment of DR.

BiP Inducer X: An ER Stress Inhibitor for Enhancing Recombinant Antibody Production in CHO Cell Culture

Prolonged endoplasmic reticulum (ER) stress reduces protein synthesis and induces apoptosis in mammalian cells. When dimethyl sulfoxide (DMSO), a specific monoclonal antibody productivity (q_mAb )-enhancing reagent, is added to recombinant Chinese hamster ovary (rCHO) cell cultures (GSR cell line), it induces ER stress and apoptosis in a dose-dependent manner. To determine an effective ER stress inhibitor, three ER stress inhibitors (BiP inducer X [BIX], tauroursodeoxycholic acid, and carbazole) are examined and BIX shows the best production performance. Coaddition of BIX (50 μm) with DMSO extends the culture longevity and enhances q_mAb . As a result, the maximum mAb concentration is significantly increased with improved galactosylation. Coaddition of BIX significantly increases the expression level of binding immunoglobulin protein (BiP) followed by increased expression of chaperones (calnexin and GRP94) and galactosyltransferase. Furthermore, the expression levels of CHOP, a well-known ER stress marker, and cleaved caspase-3 are significantly reduced, suggesting that BIX addition reduces ER stress-induced cell death by relieving ER stress. The beneficial effect of BIX on mAb production is also demonstrated with another q_mAb -enhancing reagent (sodium butyrate) and a different rCHO cell line (CS13-1.00). Taken together, BIX is an effective ER stress inhibitor that can be used to increase mAb production in rCHO cells.

The Bile Acid TUDCA Improves Beta-Cell Mass and Reduces Insulin Degradation in Mice With Early-Stage of Type-1 Diabetes

Type 1 diabetes (T1D) is characterized by impairment in beta-cell mass and insulin levels, resulting in hyperglycemia and diabetic complications. Since diagnosis, appropriate control of glycaemia in T1D requires insulin administration, which can result in side effects, such as hypoglycemia. In this sense, some bile acids have emerged as new therapeutic targets to treat T1D and T2D, as well as metabolic diseases. The taurine conjugated bile acid, tauroursodeoxycholic (TUDCA) reduces the incidence of T1D development and improves glucose homeostasis in obese and T2D mice. However, its effects in early-stage of T1D have not been well explored. Therefore, we have assessed the effects of TUDCA on the glycemic control of mice with early-stage T1D. To achieve this, C57BL/6 mice received intraperitoneal administration of streptozotocin (STZ, 40 mg/kg) for 5 days. Once diabetes was confirmed in the STZ mice, they received TUDCA treatment (300 mg/kg) or phosphate buffered saline (PBS) for 24 days. After 15 days of treatment, the STZ+TUDCA mice showed a 43% reduction in blood glucose, compared with the STZ group. This reduction was likely due to an increase in insulinemia. This increase in insulinemia may be explained, at least in part, by a reduction in hepatic IDE activity and, consequently, reduction on insulin clearance, as well as an increase in beta-cell mass and a higher beta-cell number per islet. Also, the groups did not present any alterations in insulin sensitivity. All together, these effects contributed to the improvement of glucose metabolism in T1D mice, pointing TUDCA as a potential therapeutic agent for the glycemic control in early-stage of T1D.

Fecal bile acid profile after Roux-en-Y gastric bypass and its association with the remission of type 2 diabetes in obese women: A preliminary study

OBJECTIVE

To assess the influence of Roux-en-Y gastric by-pass (RYGB) on fecal bile acid (BA) profile and its relationship with postoperative remission of type 2 diabetes (T2D).

METHODS

Fecal samples were collected 3 and 12 months after RYGB from diabetic obese women who were responsive (n = 12) and non-responsive (n = 8) to postoperative remission of T2D. Fecal BA profile was accessed by liquid chromatography coupled to tandem mass spectrometry in a targeted approach.

RESULTS

Relative to pre-operative levels, a total of 10 fecal BA profiles decreased after RYGB (ANOVA, p ≤ 0.05) with significant fold-changes for glycochenodeoxycholic, glycocholic, taurocholic, and taurochenodeoxycholic acids at 3-months postoperatively, and for glycochenodeoxycholic, glycocholic and taurocholic acids at 12 months postoperatively (Benjamini-Hochberg, p ≤ 0.05). Postoperative changes in fecal BA were different between responsive and non-responsive women, with a significant reduction in more sub-fractions of BA in responsive women than in non-responsive women, and a marked difference in the temporal behavior of cholic acid (CA) and chenodeoxycholic acid (CDCA), thus reflecting changes in CA/CDCA ratio, and tauroursodeoxycolic (TUDCA) levels between these responsiveness groups (ANOVA, p ≤ 0.05).

CONCLUSION

RYGB induces a marked reduction in the concentration of fecal BA, which is heterogeneous according to T2D responsiveness.

p38 MAPK Facilitates Crosstalk Between Endoplasmic Reticulum Stress and IL-6 Release in the Intervertebral Disc

Degenerative disc disease is associated with increased expression of pro-inflammatory cytokines in the intervertebral disc (IVD). However, it is not completely clear how inflammation arises in the IVD and which cellular compartments are involved in this process. Recently, the endoplasmic reticulum (ER) has emerged as a possible modulator of inflammation in age-related disorders. In addition, ER stress has been associated with the microenvironment of degenerated IVDs. Therefore, the aim of this study was to analyze the effects of ER stress on inflammatory responses in degenerated human IVDs and associated molecular mechanisms. Gene expression of ER stress marker GRP78 and pro-inflammatory cytokines IL-6, IL-8, IL-1β, and TNF-α was analyzed in human surgical IVD samples (n = 51, Pfirrmann grade 2-5). The expression of GRP78 positively correlated with the degeneration grade in lumbar IVDs and IL-6, but not with IL-1β and TNF-α. Another set of human surgical IVD samples (n = 25) was used to prepare primary cell cultures. ER stress inducer thapsigargin (Tg, 100 and 500 nM) activated gene and protein expression of IL-6 and induced phosphorylation of p38 MAPK. Both inhibition of p38 MAPK by SB203580 (10 µM) and knockdown of ER stress effector CCAAT-enhancer-binding protein homologous protein (CHOP) reduced gene and protein expression of IL-6 in Tg-treated cells. Furthermore, the effects of an inflammatory microenvironment on ER stress were tested. TNF-α (5 and 10 ng/mL) did not activate ER stress, while IL-1β (5 and 10 ng/mL) activated gene and protein expression of GRP78, but did not influence [Ca2+]i flux and expression of CHOP, indicating that pro-inflammatory cytokines alone may not induce ER stress in vivo. This study showed that IL-6 release in the IVD can be initiated following ER stress and that ER stress mediates IL-6 release through p38 MAPK and CHOP. Therapeutic targeting of ER stress response may reduce the consequences of the harsh microenvironment in degenerated IVD.

Endoplasmic reticulum stress signalling - from basic mechanisms to clinical applications

The endoplasmic reticulum (ER) is a membranous intracellular organelle and the first compartment of the secretory pathway. As such, the ER contributes to the production and folding of approximately one‐third of cellular proteins, and is thus inextricably linked to the maintenance of cellular homeostasis and the fine balance between health and disease. Specific ER stress signalling pathways, collectively known as the unfolded protein response (UPR), are required for maintaining ER homeostasis. The UPR is triggered when ER protein folding capacity is overwhelmed by cellular demand and the UPR initially aims to restore ER homeostasis and normal cellular functions. However, if this fails, then the UPR triggers cell death. In this review, we provide a UPR signalling‐centric view of ER functions, from the ER's discovery to the latest advancements in the understanding of ER and UPR biology. Our review provides a synthesis of intracellular ER signalling revolving around proteostasis and the UPR, its impact on other organelles and cellular behaviour, its multifaceted and dynamic response to stress and its role in physiology, before finally exploring the potential exploitation of this knowledge to tackle unresolved biological questions and address unmet biomedical needs. Thus, we provide an integrated and global view of existing literature on ER signalling pathways and their use for therapeutic purposes.

Tauroursodeoxycholic acid alleviates secondary injury in the spinal cord via up-regulation of CIBZ gene

Spinal cord injury (SCI) is generally divided into primary and secondary injuries, and apoptosis is an important event of the secondary injury. As an endogenous bile acid and recognized endoplasmic reticulum (ER) stress inhibitor, tauroursodeoxycholic acid (TUDCA) administration has been reported to have a potentially therapeutic effect on neurodegenerative diseases, but its real mechanism is still unclear. In this study, we evaluated whether TUDCA could alleviate traumatic damage of the spinal cord and improve locomotion function in a mouse model of SCI. Traumatic SCI mice were intraperitoneally injected with TUDCA, and the effects were evaluated based on motor function assessment, histopathology, apoptosis detection, qRT-PCR, and western blot at different time periods. TUDCA administration can improve motor function and reduce secondary injury and lesion area after SCI. Furthermore, the apoptotic ratios were significantly reduced; Grp78, Erdj4, and CHOP were attenuated by the treatment. Unexpectedly, the levels of CIBZ, a novel therapeutic target for SCI, were specifically up-regulated. Taken together, it is suggested that TUDCA effectively suppressed ER stress through targeted up-regulation of CIBZ. This study also provides a new strategy for relieving secondary damage by inhibiting apoptosis in the early treatment of spinal cord injury.

Co-immobilised 7α- and 7β-HSDH as recyclable biocatalyst: high-performance production of TUDCA from waste chicken bile

Chicken gallbladder has long been considered to be worthless and discarded as waste. The main composition of chicken bile is taurochenodeoxycholic acid (TCDCA), which is the isomeride of tauroursodeoxycholic acid (TUDCA). TUDCA has been effectively used for treatment of many diseases. In this paper, 7α- and 7β-hydroxysteroid dehydrogenases (HSDH) were co-immobilised on modified chitosan microspheres, and used as recyclable biocatalyst for the catalysis of chicken bile. The catalytic reaction reached equilibrium within 4 h compared with 1 h using TCDCA as substrate. After four continuous batch reactions, the conversion of TCDCA was lower than 40% and TUDCA yield was about 15% for the catalysis of chicken bile. TUDCA yield was approximately 62% after equilibrium and the content of TUDCA in reaction product was as high as 33.16%. Furthermore, the experiments showed that activity of enzymes were significantly inhibited by bilirubin, Cu²⁺ and Ca²⁺ in complex substrate. The research described not only widens the utilization of chicken bile, but also provides a clean way for the preparation of TUDCA.

TUDCA was prepared using chicken bile as substrate with the catalysis of co-immobilised 7α- and 7β-HSDH.

Targeting the enhanced ER stress response in Marinesco-Sjögren syndrome

BACKGROUND AND OBJECTIVE

Marinesco-Sjögren syndrome (MSS) is an autosomal recessive infantile-onset disorder characterized by cataracts, cerebellar ataxia, and progressive myopathy caused by mutation of SIL1. In mice, a defect in SIL1 causes endoplasmic reticulum (ER) chaperone dysfunction, leading to unfolded protein accumulation and increased ER stress. However, ER stress and the unfolded protein response (UPR) have not been investigated in MSS patient-derived cells.

METHODS

Lymphoblastoid cell lines (LCLs) were established from four MSS patients. Spontaneous and tunicamycin-induced ER stress and the UPR were investigated in MSS-LCLs. Expression of UPR markers was analyzed by western blotting. ER stress-induced apoptosis was analyzed by flow cytometry. The cytoprotective effects of ER stress modulators were also examined.

RESULTS

MSS-LCLs exhibited increased spontaneous ER stress and were highly susceptible to ER stress-induced apoptosis. The inositol-requiring protein 1α (IRE1α)-X-box-binding protein 1 (XBP1) pathway was mainly upregulated in MSS-LCLs. Tauroursodeoxycholic acid (TUDCA) attenuated ER stress-induced apoptosis.

CONCLUSION

MSS patient-derived cells exhibit increased ER stress, an activated UPR, and susceptibility to ER stress-induced death. TUDCA reduces ER stress-induced death of MSS patient-derived cells. The potential of TUDCA as a therapeutic agent for MSS could be explored further in preclinical studies.

Bile acid TUDCA improves insulin clearance by increasing the expression of insulin-degrading enzyme in the liver of obese mice

Disruption of insulin secretion and clearance both contribute to obesity-induced hyperinsulinemia, though reduced insulin clearance seems to be the main factor. The liver is the major site for insulin degradation, a process mainly coordinated by the insulin-degrading enzyme (IDE). The beneficial effects of taurine conjugated bile acid (TUDCA) on insulin secretion as well as insulin sensitivity have been recently described. However, the possible role of TUDCA in insulin clearance had not yet been explored. Here, we demonstrated that 15 days treatment with TUDCA reestablished plasma insulin to physiological concentrations in high fat diet (HFD) mice, a phenomenon associated with increased insulin clearance and liver IDE expression. TUDCA also increased IDE expression in human hepatic cell line HepG2. This effect was not observed in the presence of an inhibitor of the hepatic membrane bile acid receptor, S1PR2, nor when its downstream proteins were inhibited, including IR, PI3K and Akt. These results indicate that treatment with TUDCA may be helpful to counteract obesity-induced hyperinsulinemia through increasing insulin clearance, likely through enhanced liver IDE expression in a mechanism dependent on S1PR2-Insulin pathway activation.

Angiotensin II Causes β-Cell Dysfunction Through an ER Stress-Induced Proinflammatory Response

The metabolic syndrome is associated with an increase in the activation of the renin angiotensin system, whose inhibition reduces the incidence of new-onset diabetes. Importantly, angiotensin II (AngII), independently of its vasoconstrictor action, causes β-cell inflammation and dysfunction, which may be an early step in the development of type 2 diabetes. The aim of this study was to determine how AngII causes β-cell dysfunction. Islets of Langerhans were isolated from C57BL/6J mice that had been infused with AngII in the presence or absence of taurine-conjugated ursodeoxycholic acid (TUDCA) and effects on endoplasmic reticulum (ER) stress, inflammation, and β-cell function determined. The mechanism of action of AngII was further investigated using isolated murine islets and clonal β cells. We show that AngII triggers ER stress, an increase in the messenger RNA expression of proinflammatory cytokines, and promotes β-cell dysfunction in murine islets of Langerhans both in vivo and ex vivo. These effects were significantly attenuated by TUDCA, an inhibitor of ER stress. We also show that AngII-induced ER stress is required for the increased expression of proinflammatory cytokines and is caused by reactive oxygen species and IP3 receptor activation. These data reveal that the induction of ER stress is critical for AngII-induced β-cell dysfunction and indicates how therapies that promote ER homeostasis may be beneficial in the prevention of type 2 diabetes.

Sequestosome 1 (SQSTM1/p62) maintains protein folding capacity under endoplasmic reticulum stress in mouse hypothalamic organotypic culture

Sequestosome 1 (SQSTM1) also known as ubiquitin-binding protein p62 (p62) is a cargo protein involved in the degradation of misfolded proteins via selective autophagy. Disruption of autophagy and resulting accumulation of misfolded proteins in the endoplasmic reticulum (ER) leads to ER stress. ER stress is implicated in several neurodegenerative diseases and obesity. As knockout of p62 (p62KO) reportedly induces obesity in mice, we examined how p62 contributes to ER stress and the ensuing unfolded protein response (UPR) in hypothalamus using mouse organotypic cultures in the present study. Cultures from p62KO mice showed significantly reduced formation of LC3-GFP puncta, an index of autophagosome formation, in response to the chemical ER stressor thapsigargin compared to wild-type (WT) cultures. Hypothalamic cultures from p62KO mice exhibited higher basal expression of the UPR/ER stress markers CHOP mRNA and ATF4 mRNA than WT cultures. Thapsigargin enhanced CHOP, ATF4, and BiP mRNA as well as p-eIF2α protein expression in both WT and p62KO cultures, but all peak values were greater in p62KO cultures. A proteasome inhibitor increased p62 expression in WT cultures and upregulated the UPR/ER stress markers CHOP mRNA and ATF4 mRNA in both genotypes, but to a greater extent in p62KO cultures. Therefore, p62 deficiency disturbed autophagosome formation and enhanced both basal and chemically induced ER stress, suggesting that p62 serves to prevent ER stress in mouse hypothalamus by maintaining protein folding capacity.

Combination of tauroursodeoxycholic acid and N-acetylcysteine exceeds standard treatment for acetaminophen intoxication

BACKGROUND & AIMS

Acetaminophen overdose in mice is characterized by hepatocyte endoplasmic reticulum stress, which activates the unfolded protein response, and centrilobular hepatocyte death. We aimed at investigating the therapeutic potential of tauroursodeoxycholic acid, a hydrophilic bile acid known to have anti-apoptotic and endoplasmic reticulum stress-reducing capacities, in experimental acute liver injury induced by acetaminophen overdose.

METHODS

Mice were injected with 300 mg/kg acetaminophen, 2 hours prior to receiving tauroursodeoxycholic acid, N-acetylcysteine or a combination therapy, and were euthanized 24 hours later. Liver damage was assessed by serum transaminases, liver histology, terminal deoxynucleotidyl transferase dUTP nick end labelling staining, expression profiling of inflammatory, oxidative stress, unfolded protein response, apoptotic and pyroptotic markers.

RESULTS

Acetaminophen overdose resulted in a significant increase in serum transaminases, hepatocyte cell death, unfolded protein response activation, oxidative stress, NLRP3 inflammasome activation, caspase 1 and pro-inflammatory cytokine expressions. Standard of care, N-acetylcysteine and, to a lesser extent, tauroursodeoxycholic treatment were associated with significantly lower transaminase levels, hepatocyte death, unfolded protein response activation, oxidative stress markers, caspase 1 expression and NLRP3 levels. Importantly, the combination of N-acetylcysteine and tauroursodeoxycholic acid improved serum transaminase levels, reduced histopathological liver damage, UPR-activated CHOP, oxidative stress, caspase 1 expression, NLRP3 levels, IL-1β levels and the expression of pro-inflammatory cytokines and this to a greater extend than N-acetylcysteine alone.

CONCLUSIONS

These findings indicate that a combination strategy of N-acetylcysteine and tauroursodeoxycholic acid surpasses the standard of care in acetaminophen-induced liver injury in mice and might represent an attractive therapeutic opportunity for acetaminophen-intoxicated patients.

Unraveling the role of ER stress inhibitors in the context of metabolic diseases

ER stress is provoked by the accumulation of unfolded and misfolded proteins in the ER lumen leading to perturbations in ER homeostasis. ER stress activates a signaling cascade called the Unfolded Protein Response (UPR) which triggers a set of transcriptional and translational events that restore ER homeostasis, promoting cell survival and adaptation. If this adaptive response fails, a terminal UPR program commits such cells to apoptosis. Existing preclinical and clinical evidence testify that prolonged ER stress escalates the risk of several metabolic disorders including diabetes, obesity and dyslipidemia. There have been considerable efforts to develop small molecules that are capable of ameliorating ER stress. Few naturally occurring and synthetic molecules have already been demonstrated for their efficacy in abrogating ER stress in both in vitro and in vivo models of metabolic disorders. This review provides a broad overview of the molecular mechanisms of inhibition of ER stress and its association with various metabolic diseases.

Modulation of the Unfolded Protein Response by Tauroursodeoxycholic Acid Counteracts Apoptotic Cell Death and Fibrosis in a Mouse Model for Secondary Biliary Liver Fibrosis

The role of endoplasmic reticulum stress and the unfolded protein response (UPR) in cholestatic liver disease and fibrosis is not fully unraveled. Tauroursodeoxycholic acid (TUDCA), a hydrophilic bile acid, has been shown to reduce endoplasmic reticulum (ER) stress and counteract apoptosis in different pathologies. We aimed to investigate the therapeutic potential of TUDCA in experimental secondary biliary liver fibrosis in mice, induced by common bile duct ligation. The kinetics of the hepatic UPR and apoptosis during the development of biliary fibrosis was studied by measuring markers at six different timepoints post-surgery by qPCR and Western blot. Next, we investigated the therapeutic potential of TUDCA, 10 mg/kg/day in drinking water, on liver damage (AST/ALT levels) and fibrosis (Sirius red-staining), in both a preventive and therapeutic setting. Common bile duct ligation resulted in the increased protein expression of CCAAT/enhancer-binding protein homologous protein (CHOP) at all timepoints, along with upregulation of pro-apoptotic caspase 3 and 12, tumor necrosis factor receptor superfamily, member 1A (TNFRsf1a) and Fas-Associated protein with Death Domain (FADD) expression. Treatment with TUDCA led to a significant reduction of liver fibrosis, accompanied by a slight reduction of liver damage, decreased hepatic protein expression of CHOP and reduced gene and protein expression of pro-apoptotic markers. These data indicate that TUDCA exerts a beneficial effect on liver fibrosis in a model of cholestatic liver disease, and suggest that this effect might, at least in part, be attributed to decreased hepatic UPR signaling and apoptotic cell death.

Endoplasmic reticulum stress and the unfolded protein response in pancreatic islet inflammation

Insulin-secreting pancreatic β-cells are extremely dependent on their endoplasmic reticulum (ER) to cope with the oscillatory requirement of secreted insulin to maintain normoglycemia. Insulin translation and folding rely greatly on the unfolded protein response (UPR), an array of three main signaling pathways designed to maintain ER homeostasis and limit ER stress. However, prolonged or excessive UPR activation triggers alternative molecular pathways that can lead to β-cell dysfunction and apoptosis. An increasing number of studies suggest a role of these pro-apoptotic UPR pathways in the downfall of β-cells observed in diabetic patients. Particularly, the past few years highlighted a cross talk between the UPR and inflammation in the context of both type 1 (T1D) and type 2 diabetes (T2D). In this article, we describe the recent advances in research regarding the interplay between ER stress, the UPR, and inflammation in the context of β-cell apoptosis leading to diabetes.

A Reevaluation of the Role of the Unfolded Protein Response in Islet Dysfunction: Maladaptation or a Failure to Adapt?

Endoplasmic reticulum (ER) stress caused by perturbations in ER homeostasis activates an adaptive response termed the unfolded protein response (UPR) whose function is to resolve ER stress. If unsuccessful, the UPR initiates a proapoptotic program to eliminate the malfunctioning cells from the organism. It is the activation of this proapoptotic UPR in pancreatic β-cells that has been implicated in the onset of type 2 diabetes and thus, in this context, is considered a maladaptive response. However, there is growing evidence that β-cell death in type 2 diabetes may not be caused by a maladaptive UPR but by the inhibition of the adaptive UPR. In this review, we discuss the evidence for a role of the UPR in β-cell dysfunction and death in the development of type 2 diabetes and ask the following question: Is β-cell dysfunction the result of a maladaptive UPR or a failure of the UPR to adequately adapt? The answer to this question is critically important in defining potential therapeutic strategies for the treatment and prevention of type 2 diabetes. In addition, we discuss the potential role of the adaptive UPR in staving off type 2 diabetes by enhancing β-cell mass and function in response to insulin resistance.